1. Field of the Invention
The invention relates to a radio transmission system comprising at least one base station and at least one satellite station situated in a coverage zone of the base station in which the base station can send information to a satellite station through a down transmission channel while an up transmission channel is used in which the satellite stations axe authorized to transmit.
Such a system has important fields of application when these systems are used as private systems (as opposed to the public system). In private systems, the distribution of radio resources among users is essential for optimizing the use of the allocated radio spectrum and avoiding saturation, while providing a varied range of services.
2. Description of the Related Art
Such a system is described, for example, in the journal Commutation & Transmission, no. 2, 1989, in the article: "Les systemes de radiocommunication mobile a ressources partagees TN10-TN100-TN200" by M. Coudreuse, G. Delavoipiere, G. Duysens, B. Fino.
One of these important services is the group call which renders possible a communication between a plurality of users.
In known systems, this group call includes the intervention of at least one base station which puts the users included in this call and situated within its coverage into communication with one another. This results in a first disadvantage in that the group call leads to a considerable mobilization of resources, especially when several base stations axe involved in the group call. Another disadvantage is that quite often the group call is only meant for those speakers of the group who are close to the originator of the call (for example: a call by a taxi which requires assistance from other vehicles of the same company close to the vehicle which has broken down).